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Astronomy Research

infrared imagery, photometry and spectroscopy at isr

ISR personnel have led the image processing efforts for several recent infrared space-based astronomy surveys. Dust grains in our Milky Way and other galaxies absorb ultraviolet and visible light and re-emit it in the infrared. Thus, the infrared surveys trace the location of the dust, such as in giant molecular clouds. It is within the dense cores of these clouds, such as the Orion nebula or the Cygnus-X star forming region, that new stars are being formed. The young stars are also bright in the infrared as the the newly formed star heats the remnants of the core from which it formed (& perhaps its planetary system). The Celestial Backgrounds projects on the DoD's Midcourse Space Experiment mapped the Galactic plane at 4, 8, 12, 14, and 23 microns, as well as several star forming clouds and other galaxies. The ISR produced the 24 micron survey for Spitzer's MIPSGAL program, which also mapped the Galactic plane, and the Cygnus-X Legacy program which mapped the richest nearby massive star forming region.

In addition to dusty clouds and very young stars, cool stars and older, evolved stars can be brighter in the infrared than the visible. The cool stars with K and M spectral types tend to be bright in the infrared, with temperatures of ~2000-5000 K. Their relatively simple spectra and photometric stability make them suitable as calibration standards. Although some are variable at visible wavelengths, the majority show little or no variation in the infrared. As part of the stellar calibration program, we are investigating where the transition occurs, from variable in the visible to stable in the infrared.

The older, evolved stars are bright in the infrared in part because they are actually producing new dust in their cool, extended atmospheres. The fusion products created deep in the stellar interiors have been dredged up to the atmospheres, including carbon, oxygen, and other elements heavier than hydrogen and helium, termed 'metals'. As the stars die, their atmospheres pulsate and expand, ultimately injecting the new dust and metals back into the clouds from which new stars will form, thus enriching the interstellar medium, We are studying the dust around evolved stars in the nearby Magellanic Clouds and other small satellite galaxies where the enrichment has not been as efficient as in the Milky Way. These 'metal-poor' systems can be used as surrogates to much older, more distant galaxies in the early Universe, which are much harder to study.